Modern microelectronic and optoelectronic packages are often hermetically sealed to protect the delicate components inside from outside contamination. A basic hermetic package may comprise a box like structure surrounding the components with leads extending through the sides of the package electrically connecting the components to the outside. In the case of optical components an optical fiber may extend through the package through a sealed ferrule. The package may be filled with an inert gas such as Nitrogen or Argon to flush moisture and other harmful gases out of the package. A lid may then be fitted over the package and sealed closed.
Once sealed, the contents of the package are protected from outside contamination. However, hermetically sealed packages of this type cannot protect against harmful contaminates that may originate from within the package. One such contaminate that may be found in abundance is hydrogen (H2). In particular, hydrogen can cause a number of state changes with enclosed component materials, including formation of hydrides, and reduction of oxides. In the case of metal oxide reduction, the resulting water trace gas can itself create a significant reliability problem.
While hydrogen should not present in the initial atmosphere within the sealed package, hydrogen can and does outgas from steel (which often have an annealing step in a hydrogen atmosphere), platings (e.g., Ni/Au), and from other trapped locations, such as epoxies.
Typical hydrogen mitigation approaches are those which reduce the potential hydrogen load. These approaches include “bakeout” which involves driving trapped hydrogen off with heat, and “getting” which involves locking the hydrogen into another form such as hydride or water.
Regarding the first mitigation approach, bakeout may be time consuming and can require high temperatures incompatible with the component materials. Even for those materials which can survive the bakeout conditions, because of asymptotic nature of hydrogen bakeout, the materials typically retain some level of hydrogen that will outgas over the lifetime of the product.
With regard to the second mitigation approach, so called “hydrogen getters” have been used to absorb or “get” the out gassing hydrogen and trap it before serious harm occurs. A hydrogen getter may comprise any one of a number of materials placed within the hermetic package prior to sealing that react with hydrogen thus removing it from the atmosphere within the hermetic package. For example, certain metal alloys may react with hydrogen to form metal hydrides. These types of getters typically require high temperatures to work effectively and therefore limited in their application. Unsaturated organic compounds have also been used in conjunction with the metal Palladium (Pd). Palladium functions as a catalyst to bind hydrogen to the functional groups of the organic molecules thus removing them from the atmosphere within the hermetic package. Examples of hydrogen getters sealed within the hermetic package are disclosed for example in U.S. Pat. No. 6,203,869 to Dougherty et al. and U.S. Pat. No. 6,428,612 to McPhilmy et al.
Hydrogen getters suffer a fundamental problem of finite capacity. If the amount of hydrogen outgas exceeds the getter capacity (i.e. the getter material become saturated or totally reacted), hydrogen will remain within the enclosure. The form of hydrogen storage can itself be problematic. For example, some getters form water vapor that must be managed. Solid solution getters can flake under the strain placed on the material due to hydrogen absorption, resulting in potential particle debris that must be managed.